Determination of labile trace metals with screen-printed electrode modified by a crown-ether based membrane.

In this work, we have undertaken the construction of a screen-printed electrode modified by a specific membrane to protect the working surface from interferences during the analysis of trace metals by anodic stripping voltammetry. Different crown-ethers selected for their metals affinity have been incorporated into a membrane then deposed on the working surface of the electrode. Each modified electrode has been first tested in an acidified KNO3 10(-1) mol L(-1) solution (pH 2) doped by free Cd2+ and Pb2+ ions. The response and selectivity of the modified electrodes have been investigated according to different parameters: (i) the substrates (commercial ink or carbon based homemade ink), (ii) the electrode support (polystyrene or transparency film) and (iii) crown-ethers nature (dibenzo-24-crown-8 and tetrathiacyclododecane 12-crown-4). The influence of the substrate on the response of the electrode is clearly demonstrated. Homemade ink appears as the most appropriate substrate to modify the working surface of the screen-printed electrode by a crown-ether based membrane. The effect of the composition of the membrane has been shown too. The best membrane developed showed a detection limit of 0.6 x 10(-8) mol L(-1) for Cd and 0.8 x 10(-8) mol L(-1) for Pb and a quantification limit of 10(-8) mol L(-1) for Cd and 2 x 10(-8) mol L(-1) for Pb. This method, which integrates the extraction, preconcentration and measurement, was successfully applied to environmental samples without pretreatment.